The study has three main objectives: (1) to provide a means of predicting the clinical outlook for any patient with a ventricular septal defect, valvar aortic stenosis, or valvar pulmonary stenosis treated medically or surgically with the prediction individualized according to age, cardiac catheterization data, electrocardiographic and x-ray findings, and clinical symptoms and signs; (2) to provide a basis for evaluating the advisability of surgery in cases where the comparative merits of medical and surgical treatment are currently in doubt and to identify cases where surgery is not warranted; (3) to provide means of validating the hemodynamic status indirectly; that is, without cardiac catheterization. Such validation would be based on the electrocardiograms, roentgenograms, signs and symptoms, general characteristics and past data on the patient. Patients were admitted to the study at the time of a diagnostic cardiac catheterization, either retroactively, covering the period from July 1, 1958 to June 30, 1965, with repeat cardiac catheterization at the end of eight years, or prospectively, from July 1, 1966 to June 30, 1969, with repeat cardiac catheterization at the end of four years.